1. Field of the Invention
The present invention relates to a high-frequency discharge ignition apparatus that is utilized mainly in the operation of an internal combustion engine.
2. Description of the Related Art
In recent years, the issues such as environment preservation and fuel depletion have been raised; measures for these issues are urgently required also in the automobile industry. As an example of the measures, there exists a method in which the amount of fuel consumption is drastically improved through engine downsizing and engine weight-saving achieved by use of a supercharger.
It is known that in a high-supercharge mode, the pressure inside an engine combustion chamber becomes extremely high even when no combustion occurs and hence it is difficult in this situation to produce a spark discharge for starting combustion. One of the reasons for this is that the required voltage for causing a dielectric breakdown between the high-voltage electrode and the GND electrode of an ignition plug becomes extremely high and exceeds the withstanding voltage value of the insulating porcelain of an ignition plug. In order to solve this problem, a study for raising the withstanding voltage of insulating porcelain has been being made; however, because in the actual situation, it is difficult to secure a sufficient withstanding voltage for the requirement, a means for narrowing the gap of an ignition plug cannot help being carried out. However, when the gap of the ignition plug is narrowed, the extinguishing action by the electrodes becomes large in turn; thus, there is posed a problem that the startability and the combustion performance are deteriorated.
As a solution for this problem, an avoidance means is conceivable in which energy that exceeds the extinguishing action, i.e., the thermal energy absorbed by the electrodes is provided through spark discharge or combustion is caused at a place as remote from the electrodes as possible; for example, such an ignition apparatus as disclosed in Patent Document 1 has been proposed.
An ignition apparatus disclosed in Patent Document 1 makes it possible that a conventional ignition coil produces a spark discharge in an ignition plug GAP and a high-frequency current is made to flow into the path of the spark discharge by way of a mixer formed of a capacitor so that a high-energy spark discharge and discharge plasma that spreads wider than an ordinary spark discharge are produced.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2012-112310
The conventional ignition apparatus disclosed in Patent Document 1 is a system in which a high-frequency current is made to flow into an ignition plug by way of a high-withstanding-voltage capacitor; however, it has a problem that depending on the kind of a used ignition plug and due to a change in the environment around the ignition plug at a time when a spark discharge is produced, the discharge-maintenance condition of the path for the ignition plug spark discharge changes and hence the high-frequency current cannot stably be applied.